A new series of Regulations (522.6.6 – 522.6.8) have been introduced in the 17th Edition of the IEE Wiring Regulations concerning cables concealed in a wall or partition. These new Regulations introduce the concept of skilled person, instructed person and ordinary person.
It is now a requirement to protect cables concealed in a wall or partition (at a depth of less than 50 mm) by a 30 mA RCD where the installation is not intended to be under the supervision of a skilled or instructed person where other methods of protection, including the use of cables with an earthed metallic covering, earthed conduit/trunking or mechanical protection, cannot be employed. Irrespective of the depth, a cable in a partition where the construction includes metallic parts other than fixings shall be protected by a 30 mA RCD. For example, this means that in a domestic installation, where insulated and sheathed cables are concealed in a wall at a depth of less than 50 mm and have no mechanical protection, they need to be installed within the safe zones and protected by a 30 mA RCD.
Skilled person: A person with technical knowledge or sufficient experience to enable him/her to avoid dangers which electricity may create. Instructed person A person adequately advised or supervised by skilled persons to enable him/her to avoid dangers which electricity may create.
Ordinary person: A person who is neither a skilled person nor an instructed person.
To conform with the requirements of BS 7671, wiring systems must utilize cables complying with the relevant requirements of the applicable British Standard or Harmonized Standard. Alternatively, if equipment complying with a foreign national standard, based on an IEC Standard is to be used, the designer or other person responsible for specifying the installation must verify that any differences between that standard and the corresponding British Standard or Harmonized Standard will not result in a lesser degree of safety than that afforded by compliance with the British Standard.
The effect of environmental conditions and general characteristics around various parts of the installation must be assessed to enable suitable electrical equipment, including the wiring system, to be specified. For example, cables and equipment used in agricultural and horticultural premises should be installed away from areas or routes used by animals or be of a type to withstand such attack. Any part of the fixed installation which may be exposed to a severe impact must be able to survive it. In workshops, for example, where heavy objects are moved, installation of wiring systems in traffic routes should be avoided or localized protection must be provided. Therefore, when designing a concealed installation, the designer must select a suitable wiring system. Under the 17th Edition, depending on the type of wiring selected, the method of installation and whether the installation will be under the control of a skilled person, or instructed person or ordinary person will depend whether the concealed wiring will require RCD protection or not. For example, in a domestic installation, where insulated and sheathed cables are concealed in a wall at a depth of less than 50 mm and have no mechanical protection, they need to be installed within the safe zones and need to be protected by a 30 mA RCD. Regulations 522.6.6 and 522.6.8 are reproduced here for information. 522.6.6 A cable concealed in a wall or partition at a depth of less than 50 mm from a surface of the wall or partition shall:
(i) Incorporate an earthed metallic covering which complies with the requirements of these Regulations for a protective conductor of the circuit concerned, the cable complying with BS 5467,BS 6346, BS 6724, BS 7846, BS EN 60702-1 or BS 8436, or
(ii) Be enclosed in earthed conduit complying with BS EN 61386 and satisfying the requirements of these Regulations for a protective conductor, or
(iii) Be enclosed in earthed trunking or ducting complying with BS EN 50085 and satisfying the requirements of these Regulations for a protective conductor, or
(iv) Be mechanically protected against damage sufficient to prevent penetration of the cable by nails, screws and the like, or
(v) Be installed in a zone within 150 mm from the top of the wall or partition or within 150 mm of an angle formed by two adjoining walls or partitions. Where the cable is connected to a point, accessory or switch gear on any surface of the wall or partition, the cable may be installed in a zone either horizontally or vertically, to the point, accessory or switch gear. Where the location of the accessory, point or switch gear can be.